It is well documented that enhancing immune function to cancer can have a therapeutic effect on the disease. A major limitation of immunotherapy is the added dimension that the tumor microenvironment can be immune-suppressive to the host that harbors cancer. Recently, there have been a number of approaches to try and "supercharge" the immune system to tumor Ag(s), so that when the immune system recognizes a tumor it can overcome immune-suppression and destroy the tumor. One approach that has successfully enhanced immune function in tumor-bearing hosts has been the addition of activating antibodies or ligands to TNF-receptor family members. This grant application will focus on the immune boosting activity of the TNF-R family member OX40 (CD134), which is expressed on activated T cells. When OX40 is engaged via an exogenous source of Ab or the OX40 ligand, potent anti-tumor properties are elicited. We will try and understand how OX40 engagement enhances immune function and use this knowledge to increase anti-tumor immunity. Gene array analysis in basic immune models has provided clues to how engagement of OX40 boosts immunity. This application will use the knowledge derived from the basic immunology models to enhance OX40-mediated tumor therapy through combination therapy with the cytokines that show a common gamma-chain (IL-2, IL-7, and IL-15). These cytokine receptors were found to be increased on Ag-stimulated T cells following OX40 engagement in our preliminary DNA microarray analyses. We will also try and understand the changes in T cell gene expression that occur in a tumor microenvironment upon OX40 engagement in vivo. Finally, because the OX40 technology will be taken to clinical trials within the coming year, we will work with an established method for enhancing immune function in clinical trials (i.e. GM-CSF transfected tumors) to assess its augmentation with anti-OX40. This will provide important preclinical information for the design of future clinical trials. The specific aims of the application are; 1) To characterize the molecular events that occur following OX40 engagement within T cells isolated from a tumor microenvironment, 2) To define the roles of common gamma-chain cytokines in OX40-enhanced anti-tumor immune responses, and 3) Explore the combination of anti-OX40 and a GM-CSF secreting tumor vaccine in a preclinical setting. The ultimate goal of the application will be to enhance OX40-mediated tumor therapy by gaining a better understanding of how this receptor can increase the proinflammatory properties of T cell function. [unreadable] [unreadable]